Characterization of polymers by bubble inflation, Jens H. Christensen, Henrik K. Rasmussen, Erik M. Kjær and Carsten L. Lauridsen

In order to characterize materials using a simple and relative inexpensive method, the bubble inflation technique was modified. A polymer plate is clamped between a Teflon coated plate and a heated cylinder. By applying air through the heating plate the polymer membrane deforms into the cylinder. The top position of the membrane is monitored by fiberoptic sensors positioned in the cylinder. The pressure difference across the membrane is measured as well. The deformation in this inflation device is non-uniform and is only biaxial in the top of the deformed membrane. Due to this, the responce is modelled using a finite element method in 3D Cartesian coordinates. The K-BKZ constitutive quation is used to model the non-linear properties of the material. Using linear viscoelastic properties from oscillative shear measurements and measurements of the bubble inflation, estimetion of the strain dependence in the constitutive eqution is possible.